A gas turbine engine generally includes a compressor section, a combustion section, a turbine section, and an exhaust section. The compressor section progressively increases the pressure of a working fluid entering the gas turbine engine and supplies this compressed working fluid to the combustion section. The compressed working fluid and a fuel (e.g., natural gas) mix within the combustion section and burn in a combustion chamber to generate high pressure and high temperature combustion gases. The combustion gases flow from the combustion section into the turbine section where they expand to produce work. For example, expansion of the combustion gases in the turbine section may rotate a rotor shaft connected, e.g., to a generator to produce electricity. The combustion gases then exit the gas turbine via the exhaust section.
The turbine section includes one or more turbine nozzles, which direct the flow of combustion gases onto one or more turbine rotor blades. The one or more turbine rotor blades, in turn, extract kinetic energy and/or thermal energy from the combustion gases, thereby driving the rotor shaft. In general, each turbine nozzle includes an inner side wall, an outer side wall, and one or more airfoils extending between the inner and the outer side walls. Since the one or more airfoils are in direct contact with the combustion gases, it may be necessary to cool the airfoils.
In certain configurations, cooling air is routed through one or more inner cavities defined by the airfoils. Typically, this cooling air is compressed air bled from compressor section. Bleeding air from the compressor section, however, reduces the volume of compressed air available for combustion, thereby reducing the efficiency of the gas turbine engine.